Ophthalmological device

ABSTRACT

An ophthalmological device emits light from a measurement optical system to an eye to be examined and calculates a dimension along the eye axis of a target portion of the eye from interfering light composed of reflected light from the eye and reference light. The measurement optical system includes incidence position changing member that changes the incidence position of light emitted to the eye, and driving unit that drives the incidence position changing member so as to scan at the incidence position of emitted light in a predetermined region of the eye. The predetermined region is a region where a straight line passes through when the straight line radially extended from the cornea apex of the eye is circumferentially moved over a predetermined angle range in the case of the eye is viewed from the front.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2013-197171 filed on Sep. 24, 2013, the contents of which are herebyincorporated by reference into the present application.

TECHNICAL FIELD

A technique disclosed in the present specification relates to anophthalmological device for examining an eye to be examined, andparticularly relates to an ophthalmological device for measuring thelength (dimension) along the eye axis of a target portion (e.g., thedepth of an anterior chamber and a crystalline lens) of an eye.

DESCRIPTION OF RELATED ART

An ophthalmological device under development measures a length(dimension) along the eye axis of a target portion (e.g., the depth ofan anterior chamber and a crystalline lens) of an eye to be examined.Such an ophthalmological device includes a measurement optical systemthat emits light from a light source into an eye to be examined andguides reflected light, and a reference optical system that emits lightfrom the light source to a reference surface and guides reflected light.Based on interfering light composed of reflected light that is guided bythe measurement optical system and reflected light that is guided by thereference optical system, the anterior surface and the posterior surfaceof a target portion in the eye are located. When the anterior surfaceand the posterior surface of the target portion are located, a dimensionalong the eye axis (depth direction) of the target portion is calculatedbased on the positions of the anterior and posterior surfaces. JapanesePatent Application Publication No. 2007-37984 and Japanese PatentApplication Publication No. 2007-313208 disclose conventional examplesof such an ophthalmological device.

BRIEF SUMMARY OF INVENTION

In order to measure a dimension along the eye axis of a target portion,e.g., the depth of an anterior chamber and the thickness of acrystalline lens, it is necessary to receive light reflected from theanterior surface (front side) of the target portion and light reflectedfrom the posterior surface (back side) of the target portion. In aconventional ophthalmological device, however, it is difficult toreceive reflected light with sufficient intensity from both of theanterior and posterior surfaces of the target portion. Thus, a dimensionalong the eye axis of the target portion may not be calculated. Forexample, even if light is reflected with sufficient intensity from theanterior surface of the target portion so as to locate the anteriorsurface of the target portion, light reflected from the posteriorsurface of the target portion may not so intensive as to locate theposterior surface of the target portion. Alternatively, even if light isreflected with sufficient intensity from the posterior surface of thetarget portion, light may be reflected with insufficient intensity fromthe anterior surface of the target portion. In this case, a dimension ofa target portion of an eye to be examined cannot be calculated along theeye axis. An object of the present teachings is to provide anophthalmological device that can measure a dimension of a target portionof an eye to be examined with stability (high probability) along the eyeaxis.

An ophthalmological device disclosed in the present specification mayinclude: a light source; a measurement optical system configured to emitlight from the light source into an eye to be examined and guidereflected light; a reference optical system configured to split lightfrom the light source and generate reference light; a light receivingelement configured to receive interfering light composed of thereflected light guided by the measurement optical system and thereference light generated by the reference optical system; and anarithmetic unit configured to calculate a dimension along the eye axisof a target portion of the eye from interfering light received by thelight receiving element. The measurement optical system may include: anincidence position changing member configured to change the incidenceposition of light emitted to the eye; and a driving unit configured todrive the incidence position changing member so as to scan at theincidence position of emitted light in a predetermined region of theeye. The predetermined region is a region where a straight line passesthrough when the straight line radially extended from the cornea apex ofthe eye is circumferentially moved over a predetermined angle range inthe case of the eye is viewed from the front.

In the ophthalmological device, the incidence position changing memberis driven by the driving unit so as to change the incidence position oflight emitted to the eye and scan, in the predetermined region, thelight emitted to the eye. A keen examination by the present inventorsproved that when reflected light from the internal surfaces of the eyeincreases in intensity, a region having a predetermined positionalrelationship with the cornea apex of the eye is likely to contain theincidence position of light. Specifically, it is proved that reflectedlight is likely to increase in intensity when light is incident in aregion circumferentially extended over a predetermined angle rangerelative to the cornea apex of an eye in front view. In theophthalmological device, the predetermined region is the regioncircumferentially extended over the predetermined angle range relativeto the cornea apex of the eye in front view, and light is scanned in thepredetermined region. Thus, reflected light having sufficient intensitycan be obtained from the internal surfaces of the eye with highprobability, thereby stably specifying the positions of the internalsurfaces of the eye.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic structural diagram showing the optical system ofan ophthalmological device according to the present embodiment.

FIG. 2 is a block diagram showing the control system of theophthalmological device according to the present embodiment.

FIG. 3 shows an explanatory drawing of the function of a zero-pointadjustment mechanism.

FIGS. 4 a and 4 b show explanatory drawings of predetermined regions forscanning light from a light source and scanning lines set in thepredetermined regions.

FIG. 5 is an explanatory drawing showing the steps of processing aninterference signal waveform obtained when the optical path length of ameasurement optical system is scanned in a predetermined optical pathlength range.

FIG. 6 is a flowchart showing an example of the steps of the process ofthe ophthalmological device according to the present embodiment.

FIG. 7 shows experimental results when the positions of incidence aredetermined by experiments so as to maximize the intensity of reflectedlight from the anterior surface of a crystalline lens (right eye, lefteye).

FIG. 8 shows experimental results when the positions of incidence aredetermined by experiments so as to maximize the intensity of reflectedlight from the posterior surface of the crystalline lens (right eye,left eye).

DETAILED DESCRIPTION OF INVENTION

In an ophthalmological device disclosed in the present specification, anarithmetic unit may specify the position of the anterior surface of atarget portion and the position of the posterior surface of the targetportion from interfering light received when light emitted to an eye isscanned in a predetermined region, and the arithmetic unit may calculatea dimension along the eye axis of the target portion from the specifiedpositions. With this configuration, the interfering light obtained byscanning light in the predetermined region is used so as to stablyspecify the positions of the anterior surface and the posterior surfaceof the target portion. This can stably calculate the dimension along theeye axis of the target portion.

In the ophthalmological device disclosed in the present specification,the incidence position at the acquisition of interfering light forspecifying the position of the anterior surface of the target portionmay be different from the incidence position at the acquisition ofinterfering light for specifying the position of the posterior surfaceof the target portion. With this configuration, the positions of thesurfaces of the target portion are specified from reflected lightobtained when light is incident at different positions of incidence ofthe eye. Thus, reflected light used for specifying the positions of thesurfaces of the target portion can be sufficiently intensive. This canstably specify the positions of the surfaces of the target portion.

In the ophthalmological device disclosed in the present specification,when light emitted to the eye is scanned in the predetermined region,the arithmetic unit may specify a first incidence position where theintensity of light reflected from the anterior surface of the targetportion is maximized and a second incidence position where the intensityof light reflected from the posterior surface of the target portion ismaximized. In this case, a driving unit may further drive an incidenceposition changing member such that light emitted to the eye is scannedon a scanning line set so as to pass through the first incidenceposition and the second incidence position, and the arithmetic unit maycalculate a dimension along the eye axis of the target portion frominterfering light when light is scanned on the scanning line set so asto pass through the first incidence position and the second incidenceposition.

With this configuration, first, light emitted to the eye is scanned inthe predetermined region, and then the first incidence position and thesecond incidence position are specified. Subsequently, light emitted tothe eye is scanned on the scanning line passing through the firstincidence position and the second incidence position. Thus, when lightis scanned on the scanning line, reflected light with sufficientintensity can be received from the anterior surface of the targetportion and reflected light with sufficient intensity can be receivedalso from the posterior surface of the target portion. In other words, athickness along the eye axis of the target portion can be calculatedonly by scanning, on the scanning line, light emitted to the eye. Sincelight emitted to the eye is scanned on the scanning line in a shorttime, the eye is placed in substantially the same state when theanterior surface of the target portion is specified and when theposterior surface of the target portion is specified. Thus, a dimensionalong the eye axis of the target portion can be calculated with highaccuracy.

In the ophthalmological device disclosed in the present specification,when the eye is viewed from the front, one of the first and secondincidence positions may be located on one side of a vertical linepassing through the cornea apex of the eye, whereas the other incidenceposition may be located on the other side of the vertical line.

In the ophthalmological device disclosed in the present specification,the scanning line may include the cornea apex of the eye and have afirst section connecting the cornea apex and the first incidenceposition and a second section connecting the cornea apex and the secondincidence position. With this configuration, light emitted to the eyecan be scanned from the first incidence position to the second incidenceposition through the cornea apex. Thus, the position of the cornea apex,the position of the anterior surface of the target portion, and theposition of the posterior surface of the target portion can be obtainedat the same time only by scanning light along the scanning line. Thus,dimensions along the eye axis can be accurately obtained. For example,if the target portion is a crystalline lens, the thickness of thecrystalline lens (e.g., a dimension from the anterior surface to theposterior surface of the crystalline lens) and the depth of the anteriorchamber (e.g., a dimension from the anterior surface or the posteriorsurface of a cornea to the anterior surface of the crystalline lens) canbe obtained at the same time by setting the scanning line. In otherwords, scanning in the first section can obtain the positions of theanterior surface/posterior surface of the cornea and the anteriorsurface of the crystalline lens; meanwhile, scanning in the secondsection can obtain the positions of the anterior surface/posteriorsurface of the cornea and the posterior surface of the crystalline lens.Thus, the thickness of the crystalline lens and the depth of theanterior chamber can be obtained at the same time.

In the ophthalmological device disclosed in the present specification,when the eye is viewed from a front, the predetermined angle range is anangle range of +20° to +85° or −20° to −85° where (+) is a clockwisedirection and (−) is a counterclockwise direction with respect to areference line that is a vertical line extended upward from the corneaapex of the eye. As will be describe later, the above-mentioned anglerange makes it possible to specify the positions of the posteriorsurface and the anterior surface of the crystalline lens of the eye withstability (high probability). The properly limited angle range allows ameasurement of a length along the eye axis of the crystalline lens in ashort time.

In the ophthalmological device disclosed in the present specification,the target portion may be the depth of the anterior chamber from theanterior surface or the posterior surface of the cornea to the anteriorsurface of the crystalline lens and/or the thickness of the crystallinelens from the anterior surface to the posterior surface of thecrystalline lens. Since the normal direction of the crystalline lens isdisplaced from the optical axis of the eye, light is diagonally incidenton the crystalline lens during measurements and the intensity ofreflected light from the anterior surface and the posterior surface ofthe crystalline lens is likely to decrease. Hence, the use of theophthalmological device described in the present specification canproperly measure these portions.

In the ophthalmological device disclosed in the present specification,the incidence position changing member may be a lens disposed on theoptical axis of light emitted to the eye. In this case, the driving unitmay move the lens in a plane orthogonal to the optical axis. The use ofthe lens disposed on the optical axis can inexpensively performtwo-dimensional scanning on light emitted to the eye. The lens used asthe incidence position changing member may be, for example, one oflenses constituting a beam expander.

First Embodiment

As shown in FIG. 1, an ophthalmological device according to a firstembodiment includes a measuring unit 10 for an examination of an eye100. The measuring unit 10 includes a coherent optical system 14 thatcauses light reflected from the eye 100 and reference light to interferewith each other, an observation optical system 50 that observes ananterior eye part of the eye 100, and an alignment optical system (notshown) that aligns the measuring unit 10 with a predetermined positionalrelationship relative to the eye 100.

The coherent optical system 14 includes a light source 12, a measurementoptical system that emits light from the light source 12 into the eyeand guides reflected light, a reference optical system that emits lightfrom the light source 12 to a reference surface and guides reflectedlight, and a light receiving element 26 that receives interfering lightcomposed of reflected light that is guided by the measurement opticalsystem and reference light guided by the reference optical system.

The light source 12 is a wavelength-swept (wavelength scanning) lightsource that changes the wavelength of emitted light with a predeterminedperiod. In the present embodiment, the wavelength of light emitted fromthe light source 12 is changed; meanwhile, reflected light from an eye Eand the reference light are caused to interfere with each other andinterfering light is measured. Fourier transform on measured interferinglight (interference signal) can specify the positions of interiorportions (e.g., a crystalline lens and a retina) of the eye E. The lightsource 12 is a light source for emitting light with a wavelength of a1-μm band (e.g., about 950 nm to 1100 nm).

The measurement optical system includes a beam splitter 24, a mirror 28,a zero-point adjustment mechanism 30, a mirror 34, a beam expander 40, amirror 46, and a hot mirror 48. Light emitted from the light source 12reaches the eye 100 through the beam splitter 24, the mirror 28, thezero-point adjustment mechanism 30, the mirror 34, the beam expander 40,the mirror 46, and the hot mirror 48. Reflected light from the eye 100is guided to the light receiving element 26 through the hot mirror 48,the mirror 46, the beam expander 40, the mirror 34, the zero-pointadjustment mechanism 30, the mirror 28, and the beam splitter 24. Thezero-point adjustment mechanism 30 and the beam expander 40 will bespecifically described later.

The reference optical system includes the beam splitter 24 and areference mirror 22. Emitted from the light source 12 is partiallyreflected by the beam splitter 24, is emitted to the reference mirror22, and then is reflected by the reference mirror 22. Light reflected bythe reference mirror 22 is guided to a light receiving element 26through the beam splitter 24. The reference mirror 22, the beam splitter24, and the light receiving element 26 are disposed at fixed positionsin an interferometer 20. Thus, in the ophthalmological device of thepresent embodiment, the reference optical path length of the referenceoptical system is kept constant.

The light receiving element 26 detects interfering light composed oflight guided by the reference optical system and light guided by themeasurement optical system. The light receiving element 26 may be, forexample, a photodiode.

The observation optical system 50 emits observation light to the eye 100through the hot mirror 48 and takes an image of light reflected from theeye 100 (that is, reflected light of emitted observation light). In thiscase, the hot mirror 48 transmits light from the light source of theobservation optical system while reflecting light from the light source12 of the coherent optical system. Thus, the ophthalmological device ofthe present embodiment can simultaneously makes a measurement using thecoherent optical system and an observation of an anterior eye part bymeans of the observation optical system 50. The observation opticalsystem 50 may be an optical system used for a known ophthalmologicaldevice and thus the explanation thereof is omitted.

The zero-point adjustment mechanism 30 and the beam expander 40 that areprovided in the measurement optical system will be described below. Thezero-point adjustment mechanism 30 includes a corner cube 32 and asecond drive unit 56 (shown in FIG. 2) that moves the corner cube 32forward and backward relative to the mirrors 28 and 34. The second driveunit 56 drives the corner cube 32 along an arrow A in FIG. 1 so as tochange an optical path length from the light source 12 to the eye 100(that is, the object optical path length of the measurement opticalsystem). As shown in FIG. 3, in the case of an optical path differenceΔz between an object optical path length from the light source 12 to thedetection surface (a cornea surface in FIG. 3) of the eye 100(specifically, the light source 12 to the detection surface+thedetection surface to the light receiving element 26) and a referenceoptical path length from the light source 12 to the reference mirror 22(specifically, the light source 12 to the reference mirror 22+thereference mirror 22 to the light receiving element 26), the intensity ofinterfering light composed of light reflected from the detection surfaceand the reference light decreases as the optical path difference Δzincreases. Conversely, as the optical path difference Δz decreases, theintensity of interfering light increases. Thus, in the presentembodiment, the object optical path length is changed by the zero-pointadjustment mechanism 30, thereby changing a position where the referenceoptical path length matches the object optical path length (so-calledzero point) from the surface of a cornea 102 to the surface of a retina106.

The beam expander 40 includes a convex lens 42 disposed closer to thelight source 12, a convex lens 44 disposed closer to the eye 100, and athird drive unit 58 that moves forward and backward the convex lens 42along an optical axis (z-axis) relative to the convex lens 44 and movesthe convex lens 44 in a plane (xy plane) orthogonal to the optical axis.The convex lens 42 and the convex lens 44 are disposed on the opticalaxis and changes the focal position of incoming parallel light. In otherwords, the third drive unit 58 moves the convex lens 42 along an arrow Bin FIG. 1. Thus, the focal position of light emitted to the eye 100changes in the depth direction of the eye 100. Specifically, in a statein which a distance between the convex lens 42 and the convex lens 44 isadjusted so as to emit parallel light from the convex lens 44, theconvex lens 42 is moved in a direction that separates from the convexlens 44, the light emitted from the convex lens 44 is converged. If theconvex lens 42 is moved in a direction that approaches the convex lens44, light emitted from the convex lens 44 is diverged. This allows thefocal position of light emitted to the eye 100 to coincide with thesurface of the cornea 102 or the surface of the retina 106 of the eye100. Thus, the intensity of light reflected from the surfaces of thecornea 102 and the retina 106 can be increased so as to precisely detectthe positions of the surfaces.

The convex lens 44 can be two-dimensionally moved in the plane (xyplane) orthogonal to the optical axis relative to the convex lens 42. Inother words, the third drive unit 58 two-dimensionally drives the convexlens 44 in the plane (xy plane) orthogonal to the optical axis relativeto the convex lens 42. Thus, the incidence position of light from thelight source 12 to the eye 100 two-dimensionally changes relative to theeye 100. Specifically, in FIG. 4, a plan view of the eye 100, theincidence position two-dimensionally changes in the plane (xy plane).For example, if the convex lens 44 is moved in y direction relative tothe convex lens 42, the incidence position also changes in y direction.Furthermore, the convex lens 44 moved in x direction relative to theconvex lens 42 changes the incidence position in x direction. Thus, theconvex lens 44 moved in x direction and/or y direction relative to theconvex lens 42 changes the incidence position in the xy plane.

In the beam expander 40 of the present embodiment, the convex lens 42 ismoved along the optical axis so as to adjust the focal position oflight, and the convex lens 44 is moved in the plane orthogonal to theoptical axis so as to adjust the incidence position of light. Thepresent teachings is not limited to this configuration. For example, thefocal position of light may be changed by moving the convex lens 44instead of the convex lens 42 along the optical axis. The convex lens 42may be moved instead of the convex lens 44 in the plane orthogonal tothe optical axis so as to adjust the incidence position of light.Alternatively, the focal position of light and the incidence position oflight may be adjusted by moving one of the convex lens 42 and the convexlens 44 along the optical axis and in the plane orthogonal to theoptical axis relative to the other lens. In the present embodiment, thebeam expander 40 includes the two convex lenses 42 and 44. The beamexpander may include three or more lenses. For example, the convex lens42 may include a plurality of lenses.

As shown in FIG. 4, in the present embodiment, the third drive unit 58drives the convex lens 44 such that the incidence position of lightemitted to the eye 100 is scanned in predetermined regions 108 a and 108b. The predetermined region 108 a is a sector region extended over anangle range of θ1 to θ2 in a circumferential direction (clockwisedirection) with respect to a reference line that is a perpendicular line(y axis in FIGS. 4( a) and 4(b)) extended upward from a cornea apex 110of the eye 100. The predetermined region 108 b is a sector regionextended over an angle range of θ3 to θ4 in a circumferential direction(counterclockwise direction) with respect to the reference line (yaxis). As has been discussed, the predetermined regions 108 a and 108 bmay be regions where a straight line passes through when the straightline radially extended from the cornea apex 110 of the eye 100 iscircumferentially moved over the angle range of θ1 to θ2 or θ3 to θ4 inthe case of the eye 100 is viewed from the front. The dimensions of thepredetermined regions 108 a and 108 b in radial directions (that is, thelengths of the straight lines) may be each set at a predetermined length(e.g., about 1 mm to 3 mm) from the cornea apex.

As shown in experimental results (see FIGS. 7 and 8), if the eye 100 isa right eye, light reflected from the anterior surface of thecrystalline lens 104 has maximum intensity when the incidence positionis located in the region 108 a, whereas light reflected from theposterior surface of the crystalline lens 104 has maximum intensity whenthe incidence position is located in the region 108 b. If the eye 100 isa left eye, light reflected from the posterior surface of thecrystalline lens 104 has maximum intensity when the incidence positionis located in the region 108 a, whereas light reflected from theanterior surface of the crystalline lens 104 has maximum intensity whenthe incidence position is located in the region 108 b. Thus, by scanningthe incidence position of light emitted to the eye 100 in thepredetermined regions 108 a and 108 b, the incidence position of lightcan be efficiently specified at the maximum intensity of reflected lightfrom the anterior surface and the posterior surface of the crystallinelens 104. In the present embodiment, θ1 is +20°, θ2 is +85°, θ3 is −20°,and θ4 is −85°. In this case, (+) denotes a clockwise direction while(−) denotes a counterclockwise direction.

In the present embodiment, a plurality of scanning lines 112 are set inthe predetermined regions 108 a and 108 b so as to cover thepredetermined regions 108 a and 108 b (only one of the scanning lines112 is shown in FIG. 4( b)). As shown in FIG. 4( b), the scanning line112 is composed of a linear part extended from the cornea apex 110 inthe predetermined region 108 b and a linear part extended from thecornea apex in the predetermined region 108 a. The scanning line 112 isa straight line passing through the cornea apex 110 and thus line can becompletely scanned over the predetermined regions 108 a and 108 b.

The alignment optical system may be an optical system used for a knownophthalmological device. The alignment optical system includes adetector 60 (shown in FIG. 2) that detects the position of the corneaapex 110 of the eye 100. In the present embodiment, the cornea apexdetector 60 detects the cornea apex 110 of the eye 100, and then theposition of the measuring unit 10 (specifically, the optical systemother than the interferometer 20 in the measuring unit 10) is adjustedbased on the detection result. This locates the measuring unit 10 at apredetermined position relative to the cornea apex 110 of the eye 100.The ophthalmological device of the present embodiment includes, asmechanisms for adjusting the position of the measuring unit 10, aposition adjustment mechanism 16 (shown in FIG. 2) for adjusting theposition of the measuring unit 10 relative to the eye 100 and a firstdrive unit 54 (shown in FIG. 2) for driving the position adjustmentmechanism 16. The alignment optical system and the cornea apex detector60 can have known configurations and thus the detailed explanationthereof is omitted.

The configuration of the control system of the ophthalmological deviceaccording to the present embodiment will be described below. As shown inFIG. 2, the ophthalmological device is controlled by an arithmetic unit64. The arithmetic unit 64 includes a microcomputer (microprocessor)having a CPU, a ROM, a RAM, and so on. The arithmetic unit 64 isconnected to the light source 12, the first to third drive units 54 to58, a monitor 62, and the observation optical system 50. The arithmeticunit 64 controls on/off of the light source 12, controls the first tothird drive units 54 to 58 so as to drive the mechanisms 16, 30, and 40,and controls the observation optical system 50 to display an anterioreye part image, which is captured by the observation optical system 50,on the monitor 62. The arithmetic unit 64 is connected to the lightreceiving element 26 and receives the interference signal correspondingto the intensity of interfering light detected by the light receivingelement 26. The arithmetic unit 64 performs Fourier transform on theinterference signal from the light receiving element 26 so as to specifythe positions of the parts of the eye 100 (the anterior and posteriorsurfaces of the cornea 102, the anterior and posterior faces of thecrystalline lens 104, and the surface of the retina 106), and calculatesa dimension (e.g., the depth of an anterior chamber and the thickness ofa crystalline lens) along an eye axis of the eye 100. The arithmeticunit 64 is connected to the cornea apex detector 60 and receives asignal from the cornea apex detector 60. The arithmetic unit 64 drivesthe position adjustment mechanism 16 by means of the first drive unit 54based on the signal from the cornea apex detector 60. Processing forspecifying the positions of the parts of the eye 100 by means of thearithmetic unit 64 will be specifically described later.

The following will discuss the steps of measuring the thickness (adimension from the anterior surface to the posterior surface of thecrystalline lens 104) and the depth of the anterior chamber (a dimensionfrom the anterior surface or posterior surface of the cornea 102 to theanterior surface of the crystalline lens 104) of the crystalline lens104 by means of the ophthalmological device of the present embodiment.As shown in FIG. 6, first, an examiner operates a switch (a switch forinputting the start of measurement, not shown). At this point, thearithmetic unit 64 positions the measuring unit 10 based on the positionof the apex of the cornea 102 detected by the cornea apex detector 60(S10). In other words, the arithmetic unit 64 processes the signal fromthe cornea apex detector 60 so as to specify the position of the apex ofthe cornea 102 of the eye 100. Moreover, the arithmetic unit 64 drivesthe position adjustment mechanism 16 by means of the first drive unit 54to position the measuring unit 14 such that the apex of the cornea 102of the eye 100 is located on the optical axis of the measurement opticalsystem. This adjusts the positions of the measuring unit 10 in xydirection (vertical and horizontal directions) and z direction (forwardor backward direction) relative to the eye 100. The positioning of themeasuring unit 14 locates the apex of the cornea 102 at the center of ananterior eye part image captured by the observation optical system 50.Moreover, the arithmetic unit 64 drives the second and third drive units56 and 58 to adjust the zero-point adjustment mechanism 30 and the beamexpander 40. Thus, the focus of light emitted from the light source 12to the eye 100 is located at a predetermined position of the eye 100(e.g., the anterior surface of the crystalline lens 104). Moreover, thezero point where an object optical path length matches a referenceoptical path length is disposed at a predetermined position of the eye100 (e.g., the anterior surface of the crystalline lens 104). In stepS10, the convex lens 44 of the beam expander 40 is driven only along theoptical axis.

Subsequently, the arithmetic unit 64 sets the light emission region ofthe eye 100 (the predetermined regions 108 a and 108 b in FIG. 4) andsets the scanning lines (the scanning line 112 in FIG. 4) in thepredetermined regions (S12). Specifically, in the ophthalmologicaldevice of the present embodiment, the predetermined regions 108 a and108 b (θ1 to θ2, θ3 to θ4) corresponding to measured portions are storedin the memory of the arithmetic unit 64. Thus, the arithmetic unit 64reads the predetermined regions 108 a and 108 b from the memoryaccording to the measured portions. Subsequently, the arithmetic unit 64sets the scanning lines 112 in the predetermined regions 108 a and 108 bso as to emit light over the predetermined regions 108 a and 108 b. Inother words, all the scanning lines 112 are scanned with light from thelight source 12, leading to light emission over the predeterminedregions 108 a and 108 b from the light source. This can obtaintomographic information on the overall predetermined regions 108 a and108 b.

At the completion of the settings of the predetermined regions 108 a and108 b and the scanning line 112, the arithmetic unit 64 selects one ofthe set scanning lines 112 (S14). Subsequently, the arithmetic unit 64changes the frequency of light emitted from the light source 12;meanwhile, the arithmetic unit 64 drives the beam expander 40 by meansof the third drive unit 58 such that the incidence position of light tothe eye 100 from the light source 12 moves on the scanning line (S16).At this point, the arithmetic unit 64 processes the interference signalinputted from the light receiving element 26, thereby obtainingtwo-dimensional tomographic information at the position of the scanningline selected in step S14. Specifically, as has been discussed, when thefrequency of light emitted from the light source 12 is changed, aposition where the measuring light and the reference light interferewith each other to generate interference waves is changed in the depthdirection of the eye 100. Thus, as shown in FIG. 5, the interferencesignal outputted from the light receiving element 26 changes in signalintensity with time. This signal is generated by interference waves ofreflected light from the parts of the eye 100 (the anterior andposterior surfaces of the cornea 102, the anterior and posterior facesof the crystalline lens 104, and the surface of the retina 106) and thereference light. Thus, the arithmetic unit 64 performs Fourier transformon the signal inputted from the light receiving element 26. Thisseparates, from the signal, interference signal components of lightreflected from the parts (the anterior and posterior surfaces of thecornea 102, the anterior and posterior surfaces of the crystalline lens104, and the surface of the retina 106) of the eye 100. Hence, thearithmetic unit 64 can specify the positions of the parts of the eye100. During the processing, the scanning line 112 is scanned with lightfrom the light source 12. In other words, the arithmetic unit 64 drivesthe beam expander 40 by means of the third drive unit 58 (specifically,the convex lens 44 is driven in a plane orthogonal to the optical axis)so as to move the incidence position of light on the scanning line. Thisallows the arithmetic unit 64 to obtain two-dimensional tomographicinformation corresponding to the position of the scanning line 112. Asdescribed above, the intensity of light reflected from the parts of theeye 100 changes depending on the incidence position of light. Thus, thetwo-dimensional tomographic information obtained by scanning on thescanning line 112 may not specify the positions of the parts of the eye100 because reflected light from the parts of the eye 100 varies inintensity depending on the incidence position.

Subsequently, the arithmetic unit 64 decides if all the scanning lines112 set in step S12 have been measured as in step S16 (S18). If all thescanning lines have not been measured as in step S16 (NO in step S18),the process returns to step S14 to repeat processing from step S14. Thisobtains two-dimensional tomographic information at positionscorresponding to all the scanning lines 112 set in step S12.

If the measurement of step S16 is conducted on all the scanning lines(YES in step S18), the arithmetic unit 64 specifies, from thetwo-dimensional tomographic information on the scanning lines, theincidence position of light (hereinafter, will be called a firstposition) when light reflected from the anterior surface position of thecrystalline lens 104 of the eye 100 has maximum intensity, and theincidence position of light (hereinafter, will be called a secondposition) when light reflected from the posterior surface position ofthe crystalline lens 104 of the eye 100 has maximum intensity (S20). Asdescribed above, light reflected from the parts of the eye 100 changesdepending on the incidence position of light to the eye 100. Thus, theinterference signal obtained in light emission at an incidence positionis subjected to Fourier transform so as to separate the interferencesignal components of light reflected from the parts (the anterior andposterior surfaces of the cornea 102, the anterior and posteriorsurfaces of the crystalline lens 104, and the surface of the retina 106)of the eye 100 at the same position. The intensity of the interferencesignal component varies depending on the intensity of light reflectedfrom the corresponding surface. Thus, the arithmetic unit 64 decides anincidence position where the interference signal component correspondingto the anterior surface position of the crystalline lens 104 ismaximized. The incidence position where the interference signalcomponent is maximized will be referred to as “first incidenceposition”. Similarly, the arithmetic unit 64 decides an incidenceposition where the interference signal component corresponding to theposterior surface of the crystalline lens 104 is maximized. Theincidence position where the interference signal component is maximizedwill be referred to as “second incidence position”.

Subsequently, the arithmetic unit 64 connects a straight line thatconnects “first incidence position” specified in step S20 and the corneaapex and a straight line that connects “second incidence position”specified in step S20 and the cornea apex, setting another scanning line(S22). For example, as shown in FIG. 4( b), a first incidence position114 is specified in the predetermined region 108 b while a secondincidence position 116 is specified in the predetermined region 108 a.In this case, a scanning line 112 a is set as another scanning lineincluding a straight line connecting the first incidence position 114and the cornea apex 110 and a straight line connecting the secondincidence position 116 and the cornea apex 110.

When another scanning line 112 a is set, the arithmetic unit 64 drivesthe beam expander 40 by means of the third drive unit 58 such that theincidence position of light from the light source 12 to the eye 100moves on the scanning line 112 a while the frequency of light emittedfrom the light source 12 is changed (S24). The scanning line 112 aincludes “first incidence position” where the intensity of lightreflected from the anterior surface of the crystalline lens 104 ismaximized and “second incidence position” where light reflected from theposterior surface of the crystalline lens 104 is maximized. When lightfrom the light source 12 is incident on the apex of the cornea 102,reflected light from the anterior and posterior surfaces of the cornea102 has the maximum intensity. Thus, the interference signal obtained instep S24 includes an interference signal component that is sufficientlyintensive to specify the positions of the anterior and posteriorsurfaces of the cornea 102, an interference signal component that issufficiently intensive to specify the position of the anterior surfaceof the crystalline lens 104, and an interference signal component thatis sufficiently intensive to specify the position of the posteriorsurface of the crystalline lens 104. These interference signalcomponents are obtained during scanning of a scanning line. In otherwords, the interference signal is obtained in quite a short time andthus these interference signal components can be obtained while the eye100 is substantially kept in a constant state.

When the interference signal is obtained in step S24, the arithmeticunit 64 specifies the position of the anterior surface of thecrystalline lens 104 from the interference signal, specifies theposition of the posterior surface of the crystalline lens 104, andspecifies the position of the anterior or posterior surface of thecornea 102 (S26). As described above, the interference signal obtainedin step S24 includes the interference signal component that issufficiently intensive to specify the position of the anterior surfaceof the crystalline lens 104, the interference signal component that issufficiently intensive to specify the position of the posterior surfaceof the crystalline lens 104, and the interference signal component thatis sufficiently intensive to specify the positions of the anterior andposterior surfaces of the cornea 102. Since the interference signal isobtained in quite a short time in step S24, the eye 100 is kept insubstantially a constant state. Thus, the arithmetic unit 64 canprecisely specify the position of the anterior surface of thecrystalline lens 104, the position of the posterior surface of thecrystalline lens 104, and the positions of the anterior and posteriorsurfaces of the cornea 102. When these positions are specified, thearithmetic unit 64 calculates the thickness of the crystalline lens 104of the eye 100 (a dimension from the anterior surface to the posteriorsurface of the crystalline lens 104) and the depth of the anteriorchamber (a dimension from the anterior surface or posterior surface ofthe cornea 102 to the position of the anterior surface of thecrystalline lens 104) (S28). The calculated value is displayed on themonitor 62. As described above, the positions of the anterior andposterior surfaces of the crystalline lens 104 and the positions of theanterior and posterior surfaces of the cornea 102 are specified withhigh accuracy, thereby accurately calculating the thickness and thedepth of the anterior chamber of the crystalline lens 104.

Experimental results on scanning of positions of incidence of light overthe eyes of a plurality of persons will be described below. Thepositions of incidence include the incidence position of light whenlight reflected from the anterior surface position of the crystallinelens has the maximum intensity and the incidence position of light whenlight reflected from the posterior surface position of the crystallinelens has the maximum intensity. As shown in FIG. 7, on the anteriorsurface of the crystalline lens of a right eye, the incidence positionof light where reflected light has the maximum intensity ranged from 20°to 85° clockwise, with a few exceptions, relative to a reference lineextending upward from the cornea apex. On the anterior surface of thecrystalline lens of a left eye, the incidence position of light wherereflected light has the maximum intensity ranged from 20° to 85°counterclockwise, with a few exceptions, relative to the reference line.As shown in FIG. 8, on the posterior surface of the crystalline lens ofthe right eye, the incidence position of light where reflected light hasthe maximum intensity ranged from 20° to 85° counterclockwise, with afew exceptions, relative to the reference line. On the posterior surfaceof the crystalline lens of the left eye, the incidence position of lightwhere reflected light has the maximum intensity ranged from 20° to 85°clockwise, with a few exceptions, relative to the reference line. Thus,the predetermined regions 108 a and 108 b are set as shown in FIG. 4,efficiently specifying the position where reflected light from theanterior surface of the crystalline lens is maximized and the positionwhere reflected light from the posterior surface of the crystalline lensis maximized.

As has been discussed, in the ophthalmological device of the presentembodiment, the incidence position of light emitted to the eye 100 ischanged to specify an incidence position where the intensity of lightreflected from the anterior and posterior surfaces of a target portion(e.g., the crystalline lens 104) of the eye 100 is maximized.Subsequently, the scanning line is set so as to pass through thespecified incidence position, and then a measurement is conducted on thescanning line to calculate a dimension along the eye axis of the targetportion. This can stably calculate a dimension along the eye axis of thetarget portion of the eye. Furthermore, when a search is conducted forpositions of incidence where the intensity of reflected light ismaximized, the search is conducted in the predetermined region that islikely to contain the positions of incidence. This can efficientlysearch for positions where the intensity of reflected light ismaximized.

Moreover, in the ophthalmological device according to the presentembodiment, the incidence position of light emitted to the eye 100 ismoved using the convex lens 44 of the beam expander 40. Thus, lightemitted to the eye 100 can be scanned at a high speed by driving thesmall convex lens 44. Moreover, by using the beam expander 40, amechanism for scanning light can be manufactured at lower cost than inscanning of light with a galvanometer mirror or the like.

In the ophthalmological device of the present embodiment, the beamexpander 40 has the function of adjusting a focus and the function ofadjusting an incidence position. Thus, the beam expander 40 cancollectively have the functions of driving (moving) the lens. This canreduce the number of components and the manufacturing cost.

Specific examples of the present teachings have been described indetail, however, these are mere exemplary indications and thus do notlimit the scope of the claims. The art described in the claims includemodifications and variations of the specific examples presented above.

For example, in the foregoing embodiment, the thickness and the depth ofthe anterior chamber of the crystalline lens are calculated. Dimensionsmay be calculated along the eye axis of other portions. Unlike in theforegoing embodiment, it is not always necessary to measure thethickness and the depth of the anterior chamber of the crystalline lens.Only the thickness of the crystalline lens or the depth of the anteriorchamber may be measured. For example, if only the thickness of thecrystalline lens is measured, light may be linearly scanned on ascanning line that is set to connect the first incidence position (theposition where maximum light is reflected from the anterior surface ofthe crystalline lens) and the second incidence position (the positionwhere maximum light is reflected from the posterior surface of thecrystalline lens). Alternatively, if only the depth of the anteriorchamber is measured, light may be linearly scanned on a scanning lineset to connect the first incidence position and the cornea apex. Withthis configuration, a desired measurement can be made in a shorter time.

In the foregoing embodiment, the beam expander 40 includes the twoconvex lenses 42 and 44. The configuration is not limited to that of theembodiment. Various configurations (e.g., a combination of a concavelens and a convex lens and a combination of a convex lens and a concavelens) may be used. In other words, even in the case of a differentconfiguration including a combination of a convex lens and a concavelens, the same functions (specifically, the functions of adjusting afocal position and an incidence position) as in the present embodimentcan be obtained.

In the foregoing embodiment, the incidence position of light is changedusing the beam expander 40. Other configurations may be adopted. Forexample, a lens disposed on an optical path may be two-dimensionallydriven in a plane orthogonal to the optical path (optical axis).

In the foregoing embodiment, light is scanned in the predeterminedregions 108 a and 108 b so as to calculate a dimension along the eyeaxis of a desired portion. If a dimension cannot be calculated along theeye axis of the desired portion only by scanning light in thepredetermined regions 108 a and 108 b, a measurement may be conducted ina region (e.g., +85° to +135° and −85° to −135° (+ is a clockwisedirection and − is a counterclockwise direction)) that is set inaddition to the predetermined regions 108 a and 108 b. With thisconfiguration, a small predetermined region can be set for an initialmeasurement, allowing measurements of, for example, a thickness ontarget portions of many persons with high efficiency (in a short time).

In the foregoing embodiment, the Fourier domain interferometer is used.A time domain interferometer may be used instead.

What is claimed is:
 1. An ophthalmological device comprising: a lightsource; a measurement optical system configured to emit light from thelight source into an eye to be examined and guide reflected light; areference optical system configured to split light from the light sourceand generates reference light; a light receiving element configured toreceive interfering light composed of the reflected light guided by themeasurement optical system and the reference light generated by thereference optical system; and an arithmetic unit configured to calculatea dimension along an eye axis of a target portion of the eye frominterfering light received by the light receiving element, themeasurement optical system including: an incidence position changingmember configured to change an incidence position of light emitted tothe eye; and a driving unit configured to drive the incidence positionchanging member so as to scan at the incidence position of emitted lightin a predetermined region of the eye, wherein the predetermined regionis a region where a straight line passes through when the straight lineradially extended from a cornea apex of the eye is circumferentiallymoved over a predetermined angle range in the case of the eye is viewedfrom a front.
 2. The ophthalmological device according to claim 1,wherein the arithmetic unit specifies a position of an anterior surfaceof the target portion and a position of a posterior surface of thetarget portion from interfering light received when light emitted to theeye is scanned in the predetermined region, and the arithmetic unitcalculates a dimension along the eye axis of the target portion from thespecified positions.
 3. The ophthalmological device according to claim2, wherein an incidence position at acquisition of interfering light forspecifying the position of the anterior surface of the target portion isdifferent from an incidence position at acquisition of interfering lightfor specifying the position of the posterior surface of the targetportion.
 4. The ophthalmological device according to claim 3, whereinwhen light emitted to the eye is scanned in the predetermined region,the arithmetic unit specifies a first incidence position where intensityof light reflected from the anterior surface of the target portion ismaximized and a second incidence position where intensity of lightreflected from the posterior surface of the target portion is maximized,the driving unit further drives the incidence position changing membersuch that light emitted to the eye is scanned on a scanning line set soas to pass through the first incidence position and the second incidenceposition, and the arithmetic unit calculates a dimension along the eyeaxis of the target portion from interfering light when light is scannedon the scanning line set so as to pass through the first incidenceposition and the second incidence position.
 5. The ophthalmologicaldevice according to claim 4, wherein when the eye is viewed from thefront, one of the first and second incidence positions is located on oneside of a vertical line passing through the cornea apex of the eye,whereas the other incidence position is located on the other side of thevertical line.
 6. The ophthalmological device according to claim 5,wherein the scanning line includes the cornea apex of the eye and has afirst section connecting the cornea apex and the first incidenceposition and a second section connecting the cornea apex and the secondincidence position.
 7. The ophthalmological device according to claim 6,wherein when the eye is viewed from a front, the predetermined anglerange is an angle range of +20° to +85° or −20° to −85° where (+) is aclockwise direction and (−) is a counterclockwise direction with respectto a reference line that is a vertical line extended upward from thecornea apex of the eye.
 8. The ophthalmological device according toclaim 7, wherein the target portion is a depth of an anterior chamberfrom an anterior surface or a posterior surface of a cornea to ananterior surface of a crystalline lens and/or a thickness of thecrystalline lens from the anterior surface to a posterior surface of thecrystalline lens.
 9. The ophthalmological device according to claim 8,wherein the incidence position changing member is a lens disposed on anoptical axis of light emitted to the eye, and the driving unit moves thelens in a plane orthogonal to the optical axis.
 10. The ophthalmologicaldevice according to claim 9, wherein the incidence position changingmember is one of lenses constituting a beam expander disposed on theoptical axis of light emitted to the eye.
 11. The ophthalmologicaldevice according to claim 1, wherein when light emitted to the eye isscanned in the predetermined region, the arithmetic unit specifies afirst incidence position where intensity of light reflected from theanterior surface of the target portion is maximized and a secondincidence position where intensity of light reflected from the posteriorsurface of the target portion is maximized, the driving unit furtherdrives the incidence position changing member such that light emitted tothe eye is scanned on a scanning line set so as to pass through thefirst incidence position and the second incidence position, and thearithmetic unit calculates a dimension along the eye axis of the targetportion from interfering light when light is scanned on the scanningline set so as to pass through the first incidence position and thesecond incidence position.
 12. The ophthalmological device according toclaim 1, wherein when the eye is viewed from a front, the predeterminedangle range is an angle range of +20° to +85° or −20° to −85° where (+)is a clockwise direction and (−) is a counterclockwise direction withrespect to a reference line that is a vertical line extended upward fromthe cornea apex of the eye.
 13. The ophthalmological device according toclaim 1, wherein the incidence position changing member is a lensdisposed on an optical axis of light emitted to the eye, and the drivingunit moves the lens in a plane orthogonal to the optical axis.